[PATCH 12/15] tty: audit: Simplify first-use allocation

The first-use tty audit buffer allocation is a potential race amongst multiple attempts at 'first-use'; only one 'winner' is acceptable. The successful buffer assignment occurs if tty_audit_buf == NULL (which will also be the return from cmpxchg()); otherwise, another racer 'won' and this buffer allocation is freed. Signed-off-by: Peter Hurley <peter(a)hurleysoftware.com&gt; --- drivers/tty/tty_audit.c | 22 +++++++--------------- 1 file changed, 7 insertions(+), 15 deletions(-) diff --git a/drivers/tty/tty_audit.c b/drivers/tty/tty_audit.c index 71ba8ba..6e33e41 100644 --- a/drivers/tty/tty_audit.c +++ b/drivers/tty/tty_audit.c @@ -181,30 +181,22 @@ int tty_audit_push(void) */ static struct tty_audit_buf *tty_audit_buf_get(void) { - struct tty_audit_buf *buf, *buf2; - unsigned long flags; + struct tty_audit_buf *buf; buf = current->signal->tty_audit_buf; if (buf) return buf; - buf2 = tty_audit_buf_alloc(); - if (buf2 == NULL) { + buf = tty_audit_buf_alloc(); + if (buf == NULL) { audit_log_lost("out of memory in TTY auditing"); return NULL; } - spin_lock_irqsave(&current->sighand->siglock, flags); - buf = current->signal->tty_audit_buf; - if (!buf) { - current->signal->tty_audit_buf = buf2; - buf = buf2; - buf2 = NULL; - } - spin_unlock_irqrestore(&current->sighand->siglock, flags); - if (buf2) - tty_audit_buf_free(buf2); - return buf; + /* Race to use this buffer, free it if another wins */ + if (cmpxchg(&current->signal->tty_audit_buf, NULL, buf) != NULL) + tty_audit_buf_free(buf); + return current->signal->tty_audit_buf; } /** -- 2.6.3